1. Field of the Invention
The present invention relates to an high Tc (Critical Temperature) superconducting cable conductor employing an oxide superconductor, and more particularly, it relates to an insulated superconducting cable conductor having flexibility, which is applicable to a superconducting cable.
2. Description of the Background Art
In relation to an oxide superconductor which enters a superconducting state at the liquid nitrogen temperature, expected is application to a superconducting cable with a cooling medium of liquid nitrogen. When such application is implemented, it may be possible to simultaneously attain simplification of a thermal protection system and reduction of a cooling cost, which are necessary for a metal superconducting cable requiring high-priced liquid helium.
A number of superconducting cables have been prepared from metal superconductors, followed by increasing study of insulating materials therefor. In relation to such insulating materials, the dielectric breakdown characteristic, the dielectric characteristic and the insulating life are taken into consideration on the premise that the same are not cracked under cooling temperatures. In relation to a metal superconducting cable, however, it has not been particularly necessary to consider influence exerted on the critical current by an insulating material as employed, since a metal superconductor has relatively high mechanical strength and exhibits an extremely high critical current density at the liquid helium temperature in a state with no application of a magnetic field.
In an oxide superconducting wire such as a bismuth based oxide superconducting wire which is stabilized by silver, the critical current density at the liquid nitrogen temperature is about 1/10 that at the liquid helium temperature at present. In the oxide superconducting wire, therefore, influence exerted on the critical current by the insulating material is more significant as compared with that in the metal superconductor. Further, an oxide superconducting wire containing ceramics is inferior in resistance against mechanical strain as compared with the metal superconducting wire. When an oxide superconducting wire is subjected to remarkable bending in preparation of a cable, for example, its critical current may be extremely reduced.